\documentclass[aspectratio=141,9pt,xcolor={svgnames,x11names},fleqn,usepdftitle=false,bookmarks=true]{beamer}

\begin{frame}[plain]
	\begin{center}
		\bgroup
		aa
		\egroup
	\end{center}
\end{frame}

\begin{frame}[plain]
	\begin{center}
		\begingroup
		aa
		\endgroup
	\end{center}
\end{frame}

\end{document}
